1. Field of the Invention
The present invention relates to a stroke-variable engine, and particularly to a stroke-variable engine comprising: a main connecting rod connected at one end to a piston through a piston pin; a subsidiary connecting rod which is connected to a crankpin of a crankshaft rotatably supported in a crankcase of an engine body and which is connected to the other end of the main connecting rod; a control rod connected at one end to the subsidiary connecting rod at a position offset from a connected position of the main connecting rod; and a pivot shaft which is rotatably supported in the crankcase so as to be rotatable about an eccentric axis parallel to the crankshaft and which is connected to the other end of the control rod so that a rotational power reduced at a reduction ratio of 1/2 is transmitted from the crankshaft to the pivot shaft.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2003-314237 discloses a conventional stroke-variable engine wherein a control rod connected at one end to a subsidiary connecting rod is connected at the other end to a pivot shaft provided on a rotary shaft having an axis parallel to a crankshaft so that the stroke of a piston is varied.
In the stroke-variable engine disclosed in the Japanese Patent Application Laid-open No. 2003-314237, a valve-operating mechanism is constructed to be an OHV-type in which a rotary shaft is also used as a camshaft. If such an OHV-type valve-operating mechanism is used, not only increased is the number of parts constituting the valve-operating mechanism such as a push rod, but also the valve-operating mechanism has a relatively large weight. Therefore, it is difficult to increase the rotational speed, and a relatively large mechanical noise is generated due to a large number of contact portions between parts constituting the valve-operating mechanism.